When the cat's away, the mice will play.

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Vikings' Kalf proved this at Headby, but the scheming warrior may not get to play for too much longer.

You don't want to get on the bad side of Lagertha (Katheryn Winnick) and Ragnar (Travis Fimmel), but the Headby usurper has done just that. Once Lagertha's trusted right-hand man, Kalf (Ben Robson) took advantage of the shielfmaiden's absence and took over her estate. Now that the former husband and wife are back in Kattegat, however, the rouge Viking will have to pay during "Usurper."

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"[Kalf] is, like every Viking, incredibly ambitious. He wants to be recognized by the gods so he can go with Odin in Valhalla. He's very intelligent," Robson explained to Zap2It. "Sometimes to achieve the things you want to do, you have to upset some people,"

It appears Kalf is the flipside of Ragnar. The current King of Denmark shares his countryman's same dreams of Valhala, put power was not something Ragnar actively sought. Now that he has it however, he is more than prepared to use it. With a Paris in his sights, Ragnar certainly has the might to take down Kalf, but will he?

Find out more when Vikings airs Thursdays at 10 p.m. ET on ABC Family. Click the video below to see a preview for the series' next episode, "Usurper."